1. Field of the Invention
The present invention relates to a dissolving device in which a high molecular coagulant is gelled by adding water.
2. Description of Related Art
A coagulant which is a water-soluble polymer having a high molecular weight (for example, "DIAFLOC" produced by Diafloc Company Limited) has conventionally been used for the dehydration of sludge and the treatment of various kinds of waste water. The coagulant neutralizes the surface charge of colloids and particulate which are suspended in water to flocculate the particles thereof, and form large flocs by the absorption and crosslinking action to facilitate the settling or floatation of the suspended substances.
It is required that the coagulant is dissolved in water prior to the use and a diluted aqueous solution is prepared. The coagulant, however, is not easily dissolved in water in a short period of time, though it is water-soluble, and several hours are required to prepare a diluted aqueous solution in a single dissolving process. Generally, therefore, in such a procedure, a coagulant is first gelled, then a diluted aqueous solution is prepared. The coagulant in a gel form readily dissolves in water in several seconds.
The conventional dissolving device in which the coagulant is gelled by adding water uses a method in which, as shown in FIG. 7 of the drawings, water and the coagulant are put into a vessel of 100 m.sup.3, a rotation axis is inserted therein from the upper side, and a stirrer having a propeller shape, fixed to a lower end of said rotation axis is rotated at a low speed to gel the coagulant in a period of 30 minutes to 1 hour, and this process is repeated. (This is a low-speed stirring batch treatment.)
The conventional method, however, utilizes low-speed stirring with a propeller-shaped stirrer and requires 30 minutes to 1 hour to gel the coagulant, result in the low productivity.
If the mixture of the coagulant and water is stirred at a high speed, the coagulant is not dissolved and the mixture becomes an aggregate of half-gelled particles which makes the half-dissolved coagulant a nucleus, and a readily water-soluble property is not obtained. Furthermore, the coagulant generally develops viscosity in the mixture as the coagulant is dissolved, and this viscosity can be referred to as a barometer which shows the cohesion (the absorption and crosslinking action) after the dilution. In the mixture stirred at a high speed, the viscosity is poor, which makes the flocculating force weak after the dilution.